Printable Version
Pronunciation: dai-æd Hear it!

Part of Speech: Noun

Meaning: 1. A closely related group of two, pair, twosome, a couple, as 'a mother-child dyad'. 2. The number 2. 3. (Mathematics) An operator that is the combination of two vectors. 4. (Biology) A pair of homologous chromosomes that result from the division of a tetrad during meiosis.

Notes: Dyad refers to two closely related objects. It lies between a monad "single" and a triad "threesome". These are followed by a tetrad, pentad, and so on. The adjectives for the first three are monadic, dyadic, and triadic.

In Play: Any set of two is a dyad: "Robin Banks ran his life on a dyad of principles: never do anything illegal and never get caught." The pair must have some connection with each other: "Behavioral psychologists consider the dyad, nature and nurture, to be the root determinants of human behavior."

Word History: Today's Good Word comes from a PIE source that is present in almost all IE languages today, sometimes several words in one language. English acquired it from Latin dyad-, the stem of dyas, which was borrowed from Greek dyas "the number 2, a set of two". The same word emerged in Greek and Latin as duo "two". The Greek and Latin words were inherited by these languages from PIE dwo- "two". This word came to be Sanskrit dva, Russian and Serbian dva, Lithuanian du, Latvian divi, English two, German zwei, Albanian dy, Breton daou, Scottish Gaelic dhà, Hindi do, Bangla and Nepali du'i, Romani (Gypsy) dui, Marathi dona, and Punjabi do. (Many thanks to Wordmaster William Hupy, contributor of over 160 Good Words since 2006, for suggesting today's Good Word, a member of a most prolific PIE family.)

Dr. Goodword,

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